Some applications are mapping an object ro, and then unmaps it directly.
In such a case, we have a di that contains obsolete fsm.maps (not matching
OS mappings). The di for this unmapped object is not active,
and has no dinfo (have_dinfo == False).
(more generally, fsm.maps can contain a whole bunch of obsolete mappings).
Later on, some other libs can be mapped with a mapping overlapping
this obsolete mapping.
A di that never had its debug info loaded can really be discarded,
even if CG_(clo_keep_debuginfo).
In such a case, it is normal to have to discard a not active di.
(it might be better to keep fsm.maps in sync with the real OS
mapping, but that is a much bigger change/fix).
The FSM debug tracing was static, it is now dynamic according
to debug loglevel >= 3.
The below is an extract of the trace showing what happens.
SYSCALL[4384,1](257) sys_openat ( 4294967196, 0x4244398(/usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqeglfs.so), 524288 ) --> [async] ...
SYSCALL[4384,1](257) ... [async] --> Success(0x3)
SYSCALL[4384,1](72) sys_fcntl[ARG3=='arg'] ( 3, 2, 1 )[sync] --> Success(0x0)
SYSCALL[4384,1](5) sys_newfstat ( 3, 0x1ffefff8b0 )[sync] --> Success(0x0)
SYSCALL[4384,1](5) sys_newfstat ( 3, 0x1ffefff9c0 )[sync] --> Success(0x0)
SYSCALL[4384,1](9) sys_mmap ( 0x0, 10520, 1, 1, 3, 0 )--4384-- di_notify_mmap-0:
--4384-- di_notify_mmap-1: 0x4027000-0x4029fff r--
--4384-- di_notify_mmap-2: /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqeglfs.so
--4384-- di_notify_mmap-3: is_rx_map 0, is_rw_map 0, is_ro_map 1
--4384-- di_notify_mmap-4: noting details in DebugInfo* at 0x10024CEA10
--4384-- di_notify_mmap-6: no dinfo loaded /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqeglfs.so (no rx or no rw mapping)
--> [pre-success] Success(0x4027000)
SYSCALL[4384,1](3) sys_close ( 3 )[sync] --> Success(0x0)
SYSCALL[4384,1](11) sys_munmap ( 0x4027000, 10520 )[sync] --> Success(0x0)
^^^^ the above munmap has not cleaned up or removed anything in DebugInfo* at 0x10024CEA10
Later on, /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so is mapped
overlapping the memory where libqeglfs.so was mapped ro.
Now, this cleans up the (useless) di that never had have_dinfo true, e.g.
------ start ELF OBJECT -------------------------------------------------------
------ name = /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so
...
--4384-- Discarding syms at 0x0-0x0 in /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqeglfs.so (have_dinfo 0)
(the 0x0-0x0 in the trace is because there was never any text mapping for libqeglfs.so).
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